1. EECE.2160 ECE Application Programming
Instructor:
Dr. Michael Geiger
Fall 2018
Lecture 9:
Switch statements
While loops

2. ECE Application Programming: Lecture 9
Lecture outline
Announcements/reminders
Program 3 due Monday, 10/1
Exam 1: Friday, 10/5
Will be allowed one double-sided 8.5” x 11” note sheet
No calculators or other electronic devices allowed
Review
Range checking with if statements
Today’s lecture
Switch statements
While loops
6/30/2019
ECE Application Programming: Lecture 9

3. Review: range checking
Common application of if statements: checking to see if value falls inside/outside desired range
Value inside range  inside both endpoints
AND together tests for each endpoint
Ex: if (x >= 1 && x <= 10)
Value outside range  outside either endpoint
OR together tests for each endpoint
Ex: if (x < 1 || x > 10)
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ECE Application Programming: Lecture 9

4. ECE Application Programming: Lecture 9
switch statements
Nesting several if/else if statements can get tedious
If each condition is simply checking equality of same variable or expression, can use switch
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ECE Application Programming: Lecture 9

5. switch/case statement - General form
switch ( <expression> ) { case <value1> : <statements> [ break; ]
case <value2> : <statements> [ break; ] .
. [ default: <statements> [ break; ] ] }
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ECE Application Programming: Lecture 9

6. switch/case statement
Check if <expression> matches any value in case statements
If <expression> == <value1>, execute <statements> in that case
If <expression> == <value2>, execute <statements> in that case
If <expression> does not equal any of the values, go to default case (if present)
6/30/2019
ECE Application Programming: Lecture 9

7. Switch statements and break
Each case is just a starting point—switch does not automatically skip other cases!
Example:
switch (x) {
case 0:
x = 3;
case 1:
x = x * 4;
default:
x = x – 1; }
If x == 0:
Start at case 0  x = 3;
Then, go to case 1  x = x * 4 = 3 * 4 = 12
Then, go to default:  x = x – 1 = 12 – 1 = 11
6/30/2019
ECE Application Programming: Lecture 9

8. Switch statements and break
Use break to exit at end of case
You may not always want to use break—will see examples later
Rewriting previous example:
switch (x) {
case 0:
x = 3;
break;
case 1:
x = x * 4;
default:
x = x – 1; }
6/30/2019
ECE Application Programming: Lecture 9

9. switch/case statement - example
#include <stdio.h>
int main() { char grd; printf("Enter Letter Grade: "); scanf("%c",&grd); printf(“You are ");
// continued next slide
6/30/2019
ECE Application Programming: Lecture 9

10. switch/case statement - example
switch (grd) { case 'A' :
printf("excellent"); break; case 'B' :
printf("good"); break; case 'C' :
printf("average"); break; case 'D' :
printf("poor"); break; case 'F' :
printf("failing"); break; default :
printf(“incapable of reading directions"); break; } return 0; }
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ECE Application Programming: Lecture 9

11. Example: switch statement
What does the program on the previous slides print if the user enters: A B+ c X
Recognize, of course, that it always prints:
Enter Letter Grade:
6/30/2019
ECE Application Programming: Lecture 9

12. ECE Application Programming: Lecture 9
Example solution
What does the program on the previous slides print if the user enters: A
You are excellent B+
Only first character is read—’B’
You are good c
This program is case-sensitive—’C’ and ‘c’ are two different characters!
Will go to default case
You are incapable of reading directions X
No case for ‘X’—goes to default case
6/30/2019
ECE Application Programming: Lecture 9

13. switch/case statement - Alt example
switch (grd) { case 'A' : case 'a': case 'B' : case 'b': printf("doing very well"); break; case 'C' : case 'c': case 'D' : case 'd': printf("not doing too well"); break; case 'F' : case ‘f': printf("failing"); break; default :
printf("incapable of reading directions"); break; } return 0; }
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ECE Application Programming: Lecture 9

14. ECE Application Programming: Lecture 9
Repetition
Say we have a program to print squares of numbers between 0 and 10:
void main() {
int i; // Number to square
int iSquared; // Square of the number
printf(" i i^2\n"); // Column headings
// Compute and display the squares of numbers 0 through 10
i = 0;
iSquared = i * i;
printf("%2d%10d\n", i, iSquared);
... // Code for i = 1, 2, ... 8, 9
i = 10; }
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ECE Application Programming: Lecture 9

15. ECE Application Programming: Lecture 9
while loops
Previous program does same thing 11 times
Repetitive code can be captured in a loop
Much less code to do same amount of work
Simplest form: while loop
while (<expression>)
<statement>  loop body
Loop body will repeat as long as <expression> is true
Loop body must therefore change expression
<statement> may be one or more lines
If multiple lines, need { } to denote block
6/30/2019
ECE Application Programming: Lecture 9

16. ECE Application Programming: Lecture 9
while loops - example
x = 7; while ( x < 10 ) { printf("%d ",x); x = x + 1; }
OUTPUT:
7 8 9
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ECE Application Programming: Lecture 9

17. ECE Application Programming: Lecture 9
while loops - example
x = 7; while ( x < 3 ) { printf("%d ",x); x = x + 1; }
OUTPUT:
(no output)
Possible to have while loop body that never executes!
6/30/2019
ECE Application Programming: Lecture 9

18. Repetition with while loop
Rewriting previous program with loop
int main() {
int i; // Number to square
int iSquared; // Square of the number
printf(" i i^2\n"); // Column headings
// Compute and display the squares of numbers 0 to 10
i = 0; // Initialize i
while (i <= 10) { // Loop until i > 10
iSquared = i * i;
printf("%2d%10d\n", i, iSquared);
i = i + 1; // Increment i }
return 0;
6/30/2019
ECE Application Programming: Lecture 9

19. ECE Application Programming: Lecture 9
Final notes
Next time
More on while loops
Reminders:
Program 3 due Monday, 10/1
Exam 1: Friday, 10/5
Will be allowed one double-sided 8.5” x 11” note sheet
No calculators or other electronic devices allowed
6/30/2019
ECE Application Programming: Lecture 9